1. Department of Urology, Chase Farm Hospital, The Ridgeway, Enfield EN2 8JL, England
2. Department of Surgery and Department of Clinical Biochemistry, Royal Free and University College Medical School, Royal Free Campus, London NW3 2QG, England, and Department of Urology, Chase Farm Hospital, Enfield EN2 8JR, England
3. Department of Urology, Chase Farm Hospital, Enfield EN2 8JR, England